Antiferrolectric liquid crystal panel and method for driving same

ABSTRACT

In the driving of an antiferroelectric liquid crystal panel in which an antiferroelectric liquid crystal is inserted between a pair of substrates having a plurality of scanning electrodes and signal electrodes on the opposing surfaces thereof and there are arranged matrix forming pixels, by providing the period for bringing all the pixels simultaneously to the antiferroelectric state each time the display state of any one of the pixels is changed, the setting to the antiferroelectric state is completely carried out so that the period required for the writing of the pixels can be reduced, even if the length of the selection period for setting to the antiferroelectric state is the same as that of the selection period for setting to the ferroelectric state.

TECHNICAL FIELD

The present invention relates to an antiferroelectric liquid crystalpanel used for a liquid crystal display panel, a liquid crystal opticalshutter array, and the like, and a method for driving theantiferroelectric liquid crystal panel, more particularly to anantiferroelectric liquid crystal panel using antiferroelectric liquidcrystal and having matrix-forming pixels.

BACKGROUND ART

An antiferroelectric liquid crystal panel is known as having a wideangle of view, a capability of a high speed response, and a goodmultiplex characteristic, and the studies of the antiferroelectricliquid crystal panel have been energetically carried out. Reference canbe made to Japanese Unexamined Patent Publication (Kokai) No. 2-173724.

An antiferroelectric liquid crystal panel has a hysteresischaracteristic regarding light transmittance versus applied voltage.Accordingly, when a voltage is applied to an antiferroelectric liquidcrystal panel, if the product of the applied voltage and the appliedpulse width exceeds a threshold value, a ferroelectric state as thefirst stable state is selected, if the polarity of the applied voltageis changed, a ferroelectric state as the second stable state isselected, and if the product of the applied voltage and the appliedpulse width is below the threshold value, an antiferroelectric state asthe third stable state is selected. An example of the characteristicregarding light transmissivity versus applied voltage is shown inFIG. 1. An example of an electrode of an antiferroelectric liquidcrystal panel having matrix-forming pixels is shown in FIG. 2. Generallyin such an antiferroelectric liquid crystal panel, time-divisionaldriving is adopted in which the scanning voltages are successivelycyclically applied to the scanning electrodes Y1 to Y128, predeterminedsignal voltages are applied in parallel in synchronization with thescanning voltages to the signal electrodes X1 to X160, and the liquidcrystal molecules of the selected pixel are switched in correspondencewith the display information.

Various methods of time-divisional driving have been proposed. Examplesof the proposed methods are shown in FIGS. 3 and 4. To write one pictureplane, the writing of two frames is carried out in which the voltagevalues of the waveforms of the first frame and the second frame aresymmetrical regarding the zero voltage value, so that an alternation ofthe operation is achieved. The ON state is shown in FIG. 3, and thechanges of the voltage and the light transmissivity of pixels at thetime of setting the OFF state are shown in FIG. 4. The scanning voltageapplied to the scanning electrode consists of three phases in which inthe first phase resetting to the OFF state, i.e. the antiferroelectricstate, is carried out, in the second phase the state in the first phaseis maintained, and in the third phase selecting whether or not thesetting to the ON state, i.e. the ferroelectric state is carried out. Inthe case of FIG. 3, the setting to the ON state, i.e. the ferroelectricstate, is carried out, since the third phase of the resultant voltage asthe difference between the scanning voltage and the signal voltageexceeds the threshold voltage, while in the case of FIG. 4, the OFFstate, i.e. the antiferroelectric state, is maintained, since the thirdphase does not exceed the threshold voltage.

One of the problems in an antiferroelectric liquid crystal panel is thatthe response speed of switching from the ferroelectric state to theantiferroelectric state is twice as slow as that of switching from theantiferroelectric state to the ferroelectric state. Therefore, in theprior art method of driving, the period for resetting to theantiferroelectric state is made longer than the period for setting tothe ferroelectric state or the antiferroelectric state. However, if thenumber of the scanning electrode is increased, an disadvantage willoccur that the time for writing all the pixels is very much extended. Anobject of the present invention is to solve the disadvantages in theprior art antiferroelectric liquid crystal panel.

Also, from one of the viewpoints, if the same display is carried out fora long time according to the prior art driving method, some pixels enterthe ferroelectric liquid crystal state while other pixels never enterthe ferroelectric liquid crystal state, and, when these pixels areswitched to the antiferroelectric liquid crystal state, the differencebetween the layer structures of these pixels appears. This is becausethe pixels have different layer structures. As a result, the differencebetween the light transmittances occurs so that a disadvantage of aresidual image is brought about. An object of the present invention isto provide an antiferroelectric liquid crystal panel, havingmatrix-forming pixels, in which the residual image phenomena caused bythe difference between the layer structures of the pixels is preventedto ensure a satisfactory display.

Also, from another viewpoint, in order to carry out a satisfactorytime-divisional driving in the driving of a liquid crystal display,where the scanning side voltage value of the phase for determining thedisplay state is assumed to be V_(C) and the signal side voltage valueis assumed to be V_(D), it is necessary concerning the setting of thevoltage to satisfy regarding the first scanning period therelationships:

    |V.sub.C |+V.sub.D |≧V5

and

    0≦||V.sub.C -|V.sub.D ||≦V1

and, in the time-divisional driving, since the driving is carried outunder the condition: V_(C) >V_(D), the range of the value of V_(D) isconsiderably limited based on the above-indicated relationships in thecase where the liquid crystal material having a large difference betweenV1 and V5 is used, since the driving is carried out under the condition:V_(C) >V_(D) (see FIG. 1). Accordingly, in the case where the liquidcrystal material having a large difference between V1 and V5, the rangeof the setting of the voltage is limited within a considerably narrowallowance, and thus the satisfactory display cannot be realized. Anobject of the present invention is to set the range of the voltage valueduring the non-selection period broader than the range in the case ofthe prior art, and to provide a method for driving an antiferroelectricliquid crystal capable of displaying easily and satisfactorily even ifthe liquid crystal material has a large difference between V1 and V5.

Also, from another viewpoint, there is a premise that a molecule of anantiferroelectric liquid crystal has three stable states, in which whenno voltage is applied the state is the third stable state as anantiferroelectric state, and when a voltage higher than the thresholdvoltage Vth is applied the switching to the first stable state as aferroelectric state or to the second stable state as a ferroelectricstate, is carried out depending on the polarity of the applied voltage.In the prior art method for the driving, to switch from theferroelectric state to the antiferroelectric state, the supplied voltageis made 0 volt to cause to switch according to the nature, e.g. theviscosity, of the liquid crystal itself without any application ofexternal forces, and accordingly the response speed from theferroelectric state to the antiferroelectric state is very low. In theprior art method for the driving, the resetting to the antiferroelectricstate is necessarily carried out in the first half of the first phase S1of the selection period consisting of the first (S1), the second (S2),and the third (S3) phases, and then a selection is made whether thebringing to the ferroelectric state or the bringing to theantiferroelectric state is carried out by the select pulse in the thirdphase S3 (see FIG. 18). In this method, as described above, the responsespeed of the antiferroelectric liquid crystal from the ferroelectricstate to the antiferroelectric state is low, the bringing to thecomplete antiferroelectric state cannot take place, if the first phaseS1 as the period for the resetting is short, to prevent the satisfactorydisplay. Accordingly, the selection period is required to besufficiently long, the frame frequency is required not to be so high,the period of the writing to the display plane must be extended, and thedriving at the video rate becomes difficult. An object of the presentinvention is to carry out the resetting to the antiferroelectric state,at a high speed, perfectly, and to provide a driving method for anantiferroelectric liquid crystal element capable of high speed driving.

Also, from a further viewpoint, there is a premise that a molecule of anantiferroelectric liquid crystal has three stable states, in which, whenno voltage is applied the state is the third stable state as anantiferroelectric state, and when a voltage having the absolute valuehigher than the threshold voltage Vs is applied the switching to thefirst stable state as a ferroelectric state or to the second stablestate as a ferroelectric state, switching is carried out depending onthe polarity of the applied voltage. The switching from theferroelectric state to the antiferroelectric state is very slow. Anobject of the present invention is to carry out perfect resetting to theantiferroelectric state in the selection period, and to provide adriving method for an antiferroelectric liquid crystal element capableof a high speed display.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided a method fordriving an antiferroelectric liquid crystal panel which holds anantiferroelectric liquid crystal between a pair of substrates having onopposite surfaces thereof a plurality of scanning electrodes and signalelectrodes and has matrix-forming pixels, characterized in that there isprovided a period for bringing simultaneously all the pixelssimultaneously to the antiferroelectric state each time the displaystate of any of the pixels is changed.

According to the present invention, there is also provided anantiferroelectric liquid crystal panel which holds an antiferroelectricliquid crystal between a pair of substrates having on opposite surfacesthereof a plurality of scanning electrodes and signal electrodes and hasmatrix-forming pixels, characterized in that the antiferroelectricliquid crystals of all the pixels are brought to the ferroelectricliquid crystal state during a predetermined period.

According to the present invention, there is also provided a method fordriving an antiferroelectric liquid crystal panel which holds anantiferroelectric liquid crystal between a pair of substrates having onopposite surfaces thereof a plurality of scanning electrodes and signalelectrodes and has matrix-forming pixels, characterized in that theactual driving of the liquid crystal unit is constituted by at least twoscanning periods, each scanning period includes at least two periods: aselection period and a non-selection period, the voltage Vu of the upperlimit of the pulse wave applied during the non-selection period is setin the range between the voltage V1 at which the transmittance startsincreasing when a voltage having the same polarity as that of the pulsewave is applied to the antiferroelectric liquid crystal unit and theapplied voltage is increased and the voltage V2 at which thetransmittance starts decreasing, when the applied voltage is decreased,i.e. V2 ≦Vu≦V1, and the voltage Vd of the lower limit of the pulse waveis set in the range between the voltage V3 at which the transmittancestarts increasing when the absolute value of the voltage having thepolarity opposite to that of the voltage V1 is increased and the valueV1, i.e. V3≦Vd≦V1.

According to the present invention, there is also provided a method fordriving an antiferroelectric liquid crystal panel in which at least afirst scanning period and a second scanning period are provided, thevoltage waveforms in said first scanning period and in said secondscanning period are symmetrical with regard to 0 volt, and each of thefirst and second scanning periods has at least a selection period and anon-selection period, characterized in that a reset pulse is applied tothe scanning electrodes at the first phase of the selection period and aselect pulse is applied to the scanning electrodes in the second phaseof said selection period, the polarity of the voltage of the reset pulseis the same as that of the threshold voltage for changing the oneferroelectric state immediately preceding the selection period to theother ferroelectric state, the absolute value of the voltage of thereset pulse is higher than 0 volt and lower than the absolute value ofthe threshold voltage, and the polarities of the reset pulse and theselect pulse in the selection period are the same.

According to the present invention, there is also provided a method fordriving an antiferroelectric liquid crystal panel in which at least afirst scanning period and a second scanning period are provided, thevoltage waveforms in said first scanning period and in said secondscanning period are symmetrical with regard to 0 volt, and each of saidfirst scanning period and said second scanning period has at least aselection period and a non-selection period, characterized in that theselection period has a first, a second, and a third phases, a resetpulse is applied to the scanning electrode in the first phase of theselection period, a base voltage is applied to the scanning electrode inthe second phase of the selection period, a select pulse is applied tothe scanning electrode in the third phase of the selection period, thepolarity of the voltage of the reset pulse is the same as that of thethreshold voltage for changing the one ferroelectric state preceding tothe selection period to the other ferroelectric state, the absolutevalue of the reset pulse is higher than 0 volt and lower than theabsolute value of the threshold voltage, the voltage Vbx of the basevoltage is given by the inequality: V3<Vbx<V1, where V1 is the voltageat which the transmittance starts increasing when a positive voltage isapplied to the antiferroelectric liquid crystal element and V3 is thevoltage at which the transmittance starts increasing when a negativevoltage is applied thereto, and the polarities of the reset pulse andthe select pulse in the same selection period are the same.

In a method for driving an antiferroelectric liquid crystal panelaccording to the present invention, all the pixels are simultaneouslyreset each time a pixel is rewritten, after that the writing is carriedout for each line of the scanning electrodes, and accordingly thedriving waveforms for setting the ferroelectric state or theantiferroelectric state are successively applied to the pixels. Sincethe period for simultaneously setting all the pixels is provided, thereset period for an individual writing is either unnecessary or is onlyrequired to be short. Also, since the writing period itself for one lineof the electrode is reduced, the period for writing all the pixels canbe reduced even if the number of the scanning electrodes is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the light transmittance versus appliedvoltage characteristic of an antiferroelectric liquid crystal panel;

FIG. 2 shows an example of an electrode of an antiferroelectric liquidcrystal panel having matrix-forming pixels;

FIGS. 3 and 4 show an example of the prior art time-divisional drivingmethod;

FIG. 5 is a cross-sectional view of a liquid crystal panel according toan embodiment of the invention;

FIG. 6 shows an example of the waveform of the driving voltage appliedto the liquid crystal panel pixel;

FIG. 7 shows a liquid crystal panel according to an embodiment of theinvention;

FIG. 8 shows the waveform of the driving voltage of a liquid crystalpanel according to an embodiment of the invention;

FIGS. 9, 10, and 11 show examples of the layer structure of anantiferroelectric liquid crystal;

FIG. 12 shows the structures of the liquid crystal panel and a polarizerplate corresponding to the operations in the driving method;

FIG. 13 shows the driving waveform of the prior art to be compared withthe driving waveform in the technique according to an embodiment of theinvention;

FIG. 14 shows the driving waveform in the technique according to anembodiment of the invention;

FIG. 15 illustrates a driving method in the technique according to anembodiment of the invention;

FIG. 16 illustrates the relationship between the voltage applied to thescanning electrode and the light transmittance;

FIG. 17 illustrates the relationship between the voltage applied to thescanning electrode and the light transmittance;

FIG. 18 illustrates an example of the prior art time-divisional drivingmethod of a liquid crystal element;

FIG. 19 illustrates the state of a liquid crystal molecule;

FIG. 20 illustrates the driving method of a liquid crystal element inthe technique according to an embodiment of the invention; and

FIG. 21 shows the relationship between the voltage supplied to thescanning electrode and the light transmittance.

BEST MODE FOR CARRYING OUT THE INVENTION

The cross-sectional view of an antiferroelectric liquid crystal panelaccording to an embodiment of the present invention is shown in FIG. 5.The antiferroelectric liquid crystal panel is constituted by putting anantiferroelectric liquid crystal 46 between a pair of substrates 43 and48 to form the layer having the thickness of approximately 2 μm. Theelectrodes 44 are formed on the opposite surfaces of the substrates 43and 48, and the orientation coatings 45 and 47 are arranged on theelectrodes. On the outside of one substrate 43, the first polarizationplate 41 is arranged so that the polarization axis of the polarizationplate is parallel with the orientation processing directions of theorientation coatings 45 and 47, while on the outside of the othersubstrate 48, the second polarization plate 49 is arranged so that thepolarization axis is 90° away from that of the first polarization plate41.

An example of the waveform of the driving voltage applied to the pixelof the liquid crystal panel of FIG. 5 is shown in FIG. 6. For the liquidcrystal panel, an antiferroelectric liquid crystal panel having 128scanning electrodes and 160 signal electrodes is used. A1 and A128 inFIG. 6 correspond to the pixel A1 and the selection period consists of 2pulses. One scanning is constituted by 2 frames. The voltage of thefirst frame and the voltage of the second frame are symmetrical witheach other with regard to 0 volt. In the case of displaying the ONstate, the voltage of the second phase in the first frame selectionperiod is 30V, and the voltage of the second phase in the second frameselection period is -30V, and in the case of displaying the OFF state,the voltage of the second phase in the first frame selection period is26V, and the voltage of the second phase in the second frame selectionperiod is -26V. Under this condition, the driving is carried out withapproximate 80 ms of the scanning period of one picture. In this case,two display pictures are alternately displayed, and the pause period inwhich the voltage applied to all the pixels are made 0 volt is provided,as shown in FIG. 6, in which the pause period is made 500 μs. In thiscase, for displaying one picture based on approximately 3 seconds of thedisplay period of one picture, 40 scannings are carried out.

In the case where the driving waveforms for selecting the ON state areapplied to every pixel, since the voltage of the first phase of thefirst frame is 0 volt, the resetting to the antiferroelectric state asan OFF state is carried out, and since the voltage of the second phaseexceeds the threshold voltage for switching to the ferroelectric state,the setting to the ferroelectric state as an ON state is carried out. Inthe case where the driving waveforms for selecting the OFF state areapplied to every pixel, since the voltage of the first phase of theselection period is 0 volt, the resetting firstly to an OFF state iscarried out, and, since the subsequent second phase does not exceed thethreshold voltage for setting the ferroelectric state, theantiferroelectric state as the OFF state is maintained.

In the case of the driving method illustrated in FIG. 5 and FIG. 6, whena new display is carried out, since there exists approximate 500 μspause period where the voltage applied to all the pixels is 0 volt, itis possible to completely reset, during this period, all the pixels fromthe ferroelectric state to the antiferroelectric state. Accordingly,even if the pulse width for setting the ferroelectric state is equal tothat for setting the antiferroelectric state, it is possible to carryout the driving satisfactorily. On the contrary, in the prior artdriving method, in the case where the pixels displaying the ON state arereset to the OFF state, if the pulse width for setting theantiferroelectric state is equal to that for setting the ferroelectricstate, it is not possible to satisfactorily reset from the ferroelectricstate to the antiferroelectric state only by the first phase of theselection pulse.

In the driving method illustrated in FIG. 5 and FIG. 6, a period isprovided in which all the pixels are simultaneously turned to theantiferroelectric state each time the re-writing of the pixel is carriedout. Due to this, it is possible to make the pulse width for selectingthe antiferroelectric state to be the same as the pulse width forselecting the ferroelectric state, and it is possible to prevent thewrite period from becoming extensively long and ensure appropriatedriving, even if the number of the scanning electrode is increased.

The antiferroelectric liquid crystal panel according to anotherembodiment of the present invention is shown in FIG. 7. Regarding theliquid crystal panel, the scanning side driving circuit 12 and thesignal side driving circuit 13 are electrically connected to theantiferroelectric crystal panel 16, and, to output two differentwaveforms, the driving circuit is constituted by the display drivingwaveform outputting circuit 14 and the layer structure controllingoutput circuit 14 and the layer structure controlling output circuit 15for controlling the smectic layer in the cell. The output switchingswitch 11 is provided in the output portion of the two waveforms, sothat the outputting from either of the sides is optionally selected. Thewaveform output terminal T is provided. Accordingly, by applying thelayer structure controlling waveforms to the liquid crystal cell forseveral seconds after carrying out the same display, it is possible tomake all the pixels ferroelectric liquid crystal state, to make thelayer structure of all the pixels to become the same, and thus toprevent the residual image phenomena caused by the difference in thelayer structures from occurring.

The driving waveforms for the antiferroelectric liquid crystal panelaccording to another embodiment of the present invention are shown inFIG. 8. Liquid crystal cells having 128 scanning side electrodes and 160signal side electrodes are used (FIG. 2, FIG. 5). Y1 and Y2 in FIG. 8correspond to Y1 and Y2 in FIG. 2. In the driving waveform, oneselection period is constituted by 2 pulses. One scanning is constitutedby 2 scanning periods, and the voltage in the first scanning period andthat in the second scanning period are symmetrical with regard to 0volt. The voltage applied to the scanning electrode is 0 volt in thefirst phase of the selection period of the first scanning period, 30V inthe second phase, 30V in two phases preceding the next selection periodas the reset period, and 10V in the remaining non-selection period. Thevoltage applied to the scanning electrode is 0 volt in the first phaseof the selection period of the second scanning period, -30V in thesecond phase, -30V in two phases preceding the next selection period asthe reset period, and -10V in the remaining non-selection period. Thevoltage applied to the signal side electrode is 0 volt in the firstphase of the ON state in synchronization with the scanning electrodeside, and 6V in the second phase. The voltage applied to the signal sideelectrode is 0 volt in the first phase of the OFF state, and -6V in thesecond phase. The driving is carried out with the frame frequency ofapproximately 60 ms.

Without depending on the signal electrode in the ON or OFF state, theliquid crystal in the pixel portion is necessarily reset to theferroelectric state during the reset period, and subsequently in theselection period it is selected whether the ON state or the OFF state.Accordingly, since no difference in the layer structure exists betweenthe pixels, no residual phenomena takes place even if a new display iswritten.

Since the antiferroelectric liquid crystal has the hysteresis nature inthe transmitted light versus voltage characteristic, when a pulse waveis applied to a liquid crystal molecule, the ferroelectric state as thefirst stable state is selected if the product of the pulse width and thevoltage exceeds the threshold value, the ferroelectric state as thesecond stable state is selected based on the polarity of the appliedvoltage in accordance with the difference in the polarity of the appliedvoltage, and, from these first and second states, the antiferroelectricstate as the third stable state is selected if the absolute value of theproduct of the pulse width and the voltage is lower than a predeterminedthreshold value. The structure of the electrode of the matrix typeliquid crystal panel including an antiferroelectric liquid crystal isshown in FIG. 2. The time-divisional driving is carried out by applyingsuccessively and periodically the selection signals to the scanningelectrodes Y1 to Y128, applying predetermined information signals inparallel to the signal electrodes X1 to X16 in synchronization with thescanning electrode signal, and switching the liquid crystal molecules ofthe selected pixels in accordance with the display information. Forexample, the methods illustrated in FIG. 3 and FIG. 4 are proposed forthe time-divisional driving. In the drivings illustrated in FIG. 7 andFIG. 8, even if the same display is displayed for a long period, noresidual imaging of the preceding picture occurs, so that a satisfactorydisplay can be realized.

Examples of the layer structure of the antiferroelectric liquid crystalare shown in FIG. 9, FIG. 10, and FIG. 11. The antiferroelectric liquidcrystal between the glass substrates G has the layer structure due tothe smectic layer S, in which, in the antiferroelectric liquid crystalstate before applying the voltage, the normal line of the substrate andthe normal line of the layer are arranged not to be orthogonal in thecell to form a chevron structure in which the layers are bent in thecell (FIG. 9). In the ferroelectric liquid crystal state after applyingthe voltage, the book-shelf type layer structure is formed in which thenormal of the substrate is orthogonal to the normal of the layer (FIG.10), and after that when the state becomes again the antiferroelectricstate, the layer structure is different from that in the beginningantiferroelectric liquid crystal state (FIG. 11). This is described in,for example, the publication OYO BUTSURI, vol. 50, No. 10. Therefore, inthe prior art driving method, if the same display is displayed for along period, both the pixels which are in the ferroelectric liquidcrystal state and the pixels which are never in the ferroelectric statewill exist. Accordingly, when these pixels are switched again to theantiferroelectric state, different layer structures of the liquidcrystal appear in the plurality of pixels. This is because the pluralityof pixels have different layer structures shown in FIG. 9 and FIG. 11.Due to this, there occurs different light transmittance, which cause theviewing of the residual image.

Examples of the operations in the driving method of theantiferroelectric liquid crystal display are illustrated in FIG. 1. Inthe operations illustrated in FIG. 1, the actual driving of theantiferroelectric liquid crystal panel consists of two scanning periods,and each scanning period has at least two period, i.e. the selectionperiod and the non-selection period. The level Vu of the upper limit ofthe pulse wave applied during the non-selection period is set in therange V2 ≦Vu≦V1, where V1 is the voltage at which the transmittancestarts increasing in the case where the voltage, having the samepolarity as the pulse width, is increased, and V2 is the voltage atwhich the transmittance starts decreasing in the case where the voltageis decreased. Also the level Vd of the lower limit of the pulse wave isset in the range V3 ≦Vd≦V2, where V3 is the voltage at which thetransmittance start increasing in the case where the absolute value ofthe voltage having the polarity opposite to that of the voltage V1 isincreased.

In the non-selection period, the three stable states set in theselection period must be maintained. For example, in the first stablestate, the voltage applied during the non-selection period is requiredto be higher than the hysteresis loop voltage V2 and lower than thevoltage V1. In the case of the first stable state, when the voltage ofthe subsequently applied pulse wave is lower than V2 and higher than V3,the state is changed to the third state. If, after this pulse wave ofthe voltage lower than V2 and higher than V3, the pulse wave of thevoltage between V1 and V2 is applied in the period sufficiently shorterthan the period necessary for the liquid crystal molecule to return tothe third stable state, it is proved that no return from the firststable state to the third stable state occurs. Since, in the usualantiferroelectric liquid crystal, the period to switch from the first orsecond stable state to the third stable state is longer than that fromthe third stable state to the first or second state, the pulse width ofone pulse applied under the non-selection condition is too short toswitch from the first stable state to the third stable state.

In the prior art, when, for example, the first stable state is selected,since the range of the voltage applied under the non-selection conditionis required to be higher than V2 and lower than V1, the range of thevoltage was limited. In the operation illustrated in FIG. 1, since therange of the lower limit of the voltage applied under the non-selectioncondition is required simply lower than V1 and higher than V3, the rangeof the voltage can be extended. For example, in the case of FIG. 1, ifthe inequality |V1-V2|≧|V2-V4| is realized, when the holding voltageunder the non-selection condition for the scanning side voltage is V2,the upper limit voltage of the pulse wave during the non-selectionperiod can be increased up to V1, and the lower limit voltage can be thevalue: V2-(|V1-V2|), and accordingly the width of the signal sidevoltage can be wider than that in the prior art.

In the time-divisional driving, the smaller the difference is betweenthe absolute value of the selection pulse applied during the selectionperiod of the scanning side voltage waveform and the absolute value ofthe signal side voltage waveform, the larger is the difference betweenthe voltage of the pulse wave applied to the pixel in the selection ofthe ON state and that in the selection of the OFF state, to facilitateto drive the liquid crystal material which does not have sharp risingand falling characteristic of the hysteresis loop. Accordingly, thegreater the absolute value of the signal side voltage, the moresatisfactory the driving. In the operation illustrated in FIG. 1, theabsolute value of the signal side voltage can be increased so that thesatisfactory display for various kinds of the liquid crystal materialcan be easily carried out.

As an example of the operation illustrated in FIG. 1, theantiferroelectric liquid crystal has the characteristic of thehysteresis loop shown in FIG. 1 where V1=18V, V2=4V, V3=-18V, V4=-4V,V5=30V, and V6=-30V. The driving waveform using this antiferroelectricliquid crystal is shown in FIG. 15. The driving waveform consists of 2scanning periods, and one selection period is constituted by 4 pulses.The voltages in the first scanning period and the second scanning periodare symmetrical to each other with regard to 0 volt. Each pulse has thewidth of 100 μs. In the first scanning period, the voltages applied tothe scanning for the first to the third phases of the selection periodare 0 volt, and that for the fourth phase is 30V, and, in the remainingnon-selection period, the waveform of 4.5V is applied as the holdingvoltage. In the second scanning period, the applied voltages for thefirst to the third phases of the selection period are 0 volt, and thatfor the fourth period is -30V, and, in the remaining non-selectionperiod, the waveform of -4.5V is applied as the holding voltage. To thesignal side electrode, in the ON state, the voltage waveforms of 0 voltfor the first and the second phases, 12V for the third phase, and -12Vfor the fourth phase are applied in synchronization with the scanningelectrode side. Also, in the OFF state, the voltage waveforms of 0 voltfor the first and the second phases, -12V for the third phase, and 12Vfor the fourth phase are applied. The driving was carried out with theframe frequency of approximately 60 ms. Accordingly, the signal sidevoltage can be set higher than that in the prior art, and the holdingvoltage of the scanning side voltage under the non-selection conditioncan be set lower, so that a satisfactory display can be carried out.

The constitution of the antiferroelectric liquid crystal as used as adisplay is shown in FIG. 12. The liquid crystal 22 is arranged betweenthe polarizer plates 21a and 21b aligned with the cross Nicol prism inthe manner that the polarization axis of either polarizer plate isparallel with the longitudinal axis direction of the molecule withoutvoltage application, so that black is displayed when no voltage isapplied and white when a voltage is applied. The characteristic of suchcell structure regarding the applied voltage versus the transmittancechange is expressed by the hysteresis loop shown in FIG. 1, in which V1is the voltage at which the transmittance starts changing as the appliedvoltage is increased, V5 is the voltage at which the transmittancechange is saturated, V2 is the voltage at which the transmittance startschanging as the applied voltage is decreased, V3 is the voltage at whichthe transmittance starts changing as the absolute value of the voltagehaving the polarity opposite to that of the above-mentioned voltage isapplied, V6 is the voltage at which the transmittance change issaturated, and V4 is the voltage at which the transmittance startschanging as the absolute value of the voltage is decreased. As will beunderstood from FIG. 1, in the application of a pulse wave to the liquidcrystal molecule, if the product of the pulse width and the voltageexceeds the threshold voltage, the ferroelectric state as the firststable state is selected, the ferroelectric state as the second stablestate is selected depending on the polarity of the applied voltage, andif the absolute value of the product of the pulse width and the voltageis lower than a predetermined threshold value based on the first and thesecond state, the antiferroelectric state as the third stable state isselected.

Various methods have been proposed for the time-divisional drivingmethod. The constitution of the electrode of the matrix type liquidcrystal panel including an antiferroelectric liquid crystal is shown inFIG. 2. The time-divisional driving in which the selection voltages aresuccessively and periodically applied to the scanning electrodes Y1 toY128, predetermined information signals are applied in parallel to thesignal electrodes X1 to X160 in synchronization with the scanningelectrode signals, and the liquid crystal molecules of the selectedpixel are switched in accordance with the display information. In thedriving method illustrated in FIG. 14, the writing of two scanningperiods is carried out to write one picture, and the voltages of thewaveforms in the first and the second scanning periods are symmetricaleach other with regard to 0 volt, so that the realization of thealternation is intended. The changes in the voltage waveform and thetransmittance of the pixel when the ON state and the OFF state of thepixel portion A1 in the arrangement of FIG. 2 is illustrated in FIG. 14.In the selection period, the signal applied to the scanning electrode Y1consists of three phases, in which in the first phase the state isnecessarily reset once to the OFF state as the antiferroelectric state,in the second phase the state in the first phase is maintained, and inthe third phase the selection whether or not the state is set to the ONstate as the ferroelectric state is carried out. If the third phaseexceeds the threshold voltage for setting the ferroelectric state, thestate is set to the ON state as the ferroelectric state, and if thethird phase does not exceed this threshold voltage, the state ismaintained in the OFF state as the antiferroelectric state.

In this case, the voltage in the non-selection period for thetime-divisional driving is set lower than the voltage V1 at which thetransmittance starts changing as the applied voltage illustrated in FIG.1 is increased, and higher than V2 at which the transmittance startschanging as the absolute value of the applied voltage is decreased.

To carry out satisfactory time-divisional driving, when the scanningside voltage is V_(C) and the signal side voltage is V_(D), regardingthe first scanning period, the inequalities |V_(C) |+|V_(D) |≧V5 and0≦||V_(C) |-|V_(D) ||≦V1 are required to be satisfied. Therefore, sincethe time-divisional driving is carried out in general under thecondition V_(C) >V_(D), if the liquid crystal material having a largedifference between V1 and V5, the range of the value V_(D) isconsiderably limited. Thus, if the liquid crystal material has a largedifference between V1 and V5, the range of setting the voltage isconsiderably limited, and accordingly the satisfactory display isdifficult to be carried out. In the driving method according to anembodiment of the present invention, by setting the range of the voltagein the non-selection period broader than that in the prior art case, thedriving of the antiferroelectric liquid crystal capable of thesatisfactory display, even for liquid crystal materials having a largedifference between V1 and V5, is realized. In the driving methodaccording to an embodiment of the present invention, for theantiferroelectric liquid crystal display, satisfactory display is easilycarried out without being affected by the characteristic of theantiferroelectric liquid crystal material used.

A method for driving an antiferroelectric liquid crystal elementaccording to an embodiment of the present invention is illustrated inFIG. 15. In the method illustrated in FIG. 15, at least the firstscanning period and the second scanning period are arranged, thewaveforms of the voltages in the first scanning period and the secondscanning period are symmetrical with regard to 0 volt, and each of thefirst scanning period and the second scanning period has the selectionperiod and the non-selection period. In the first phase of the selectionperiod a reset pulse is applied to the scanning electrode, and in thesecond phase of the selection period a select pulse is applied to thescanning electrode. The polarity of the voltage of the reset pulse isthe same as the polarity of the threshold voltage which changes thestate from the one ferroelectric state of the state before the selectionperiod to the other ferroelectric state. The absolute value of thevoltage of the reset pulse is smaller than the absolute value of thethreshold voltage and larger than 0 volt, and the polarities of thereset pulse and the select pulse in the same selection period are thesame.

As shown in FIG. 1, in the case where the switching of theantiferroelectric liquid crystal from the ferroelectric state as thefirst stable state to the ferroelectric state as the second stable stateis carried out, high speed switching can be attained by applying thevoltage having the absolute value higher than the threshold voltage V6and the same polarity as that of the threshold voltage V6. In the casewhere the antiferroelectric liquid crystal is switched from the secondstable state to the first stable state, a high speed switching can becarried out by applying the voltage having the absolute value higherthan the threshold voltage V5 and the same polarity as the thresholdvoltage V5. In this case, the liquid crystal molecule necessarily passesthrough the antiferroelectric state as the third stable state during thetransfer from the one ferroelectric state as the first or the secondstable state to the other ferroelectric state as the second or the firststable state. It has been proved that, if the voltage having the samepolarity as the threshold voltages V5 and V6 and the absolute valuelower than those of the threshold values V6 and V5 and higher than 0volt, the liquid crystal molecule can not safely transfer to the firstor the second stable state and subsequently transfers to theantiferroelectric state as the third stable state.

To carry out a high speed switching from the ferroelectric state as thefirst stable state to the antiferroelectric state as the third stablestate by utilizing this phenomena, a voltage having the same polarity asthe threshold voltage V6 required for switching to the otherferroelectric state as the second stable state and the absolute valuelower than that of the threshold voltage V6 and higher than 0 volt is tobe applied. Similarly, to carry out a high speed switching from theferroelectric state as the second stable state to the antiferroelectricstate as the third stable state, a voltage having the same polarity asthe threshold voltage V5 required for switching to the otherferroelectric state as the first stable state and the absolute valuelower than that of the threshold voltage V5 and higher than 0 volt is tobe applied. Due to this, the state of the liquid crystal molecule stopsat the antiferroelectric state so that a high speed switching from theferroelectric state as the first or the second stable state to theantiferroelectric state as the third stable state can be carried out. Inthis method, the reset pulse Vrp is applied as above. Accordingly, thepolarity of the select pulse Vs for setting from the antiferroelectricstate of the first phase Sa to the ferroelectric state or theantiferroelectric state as the next state is the same as that of thereset pulse Vrp.

The waveforms of the voltage in the case of setting the ON state for thewhite display and the OFF state for the black display are shown in FIG.15. The writing of one picture is carried out in the first scanningperiod Se and the second scanning period Sf. The waveforms in the firstscanning period Se and the second scanning period are symmetrical eachother with regard to 0 volt. Each of the first scanning period Se andthe second scanning period Sf consists of the selection period Sc andthe non-selection period Sd. The selection period is constituted by thefirst phase Sa and the second phase Sb. The reset pulse Vrp is appliedin the first phase Sa to the scanning period, and the select pulse Vs isapplied in the second phase Sb.

In the case where the ferroelectric state, i.e. the white display state,is maintained, the first or the second stable state of the stable stateis different for each of the scanning periods Se and Sf. However, if thestate immediately preceding the selection period Sc is the first stablestate, a high speed resetting to the antiferroelectric state can becarried out by making the polarity of the reset pulse Vrp to be the sameas that of the threshold voltage V6 to the second stable state, andmaking the voltage of the reset pulse Vrp to satisfy the inequality|V6|>|Vrp|>0. If the state immediately preceding the selection period isthe second stable state, a high speed resetting to the antiferroelectricstate can be carried out by making the polarity of the reset pulse Vrpto be the same as that of the threshold voltage V5 to the first stablestate, and making the voltage of the reset pulse Vrp satisfy theinequality |V5|>|Vrp|>0. If the state immediately preceding theselection period is the antiferroelectric state, since the voltage ofthe reset pulse Vrp lies in the above-mentioned range, the voltage ofthe reset pulse does not exceed the threshold voltage V5 or V6, so thatno switching to the ferroelectric state takes place. Accordingly,regardless of the state preceding immediately to the selection periodSc, the complete resetting to the antiferroelectric state is carried outin the period of the first phase which is the period for applying thereset pulse Vrp, so that the frequency of the frame frequency can beenhanced. Also, due to this, driving at the video rate without a delayin the writing of the picture can be carried out.

The relationship between the voltage applied to the scanning electrodeand the light transmittance in the selection period Sc of the ON statefor the white display is illustrated in FIG. 10. The selection period isconstituted by the first phase Sa and the second phase Sb. In the firstphase Sa the reset pulse Vrp is applied, and in the second phase Sb theselect pulse Vs is applied. The state immediately preceding theselection period Sc is the ferroelectric state. In this embodiment,since the complete resetting to the antiferroelectric state is carriedout in the period of the first phase Sa, the light transmittance issufficiently low immediately before applying the select pulse Vs.

As a comparison, the relationship between the voltage applied to thescanning electrode and the light transmittance in the prior art drivingmethod is shown in FIG. 17. As shown in FIG. 17, no sufficient resettingto the antiferroelectric state is carried out in the period of the firstphase S1 and the second phase S2 of the selection period S4.

The relationship between the applied voltage and the light transmittanceof the liquid crystal panel in this embodiment is shown in FIG. 1 inwhich the threshold voltage V5 is 40V, and the threshold voltage V6 is-40V.

The reset pulse Vrp is applied to the scanning electrode in the firstphase Sa, and the select pulse Vs is applied to the second phase Sb. Thevoltage of the reset pulse Vrp in the first scanning period Se is set to18V, the voltage of the select pulse Vs is set to 30V, and the holdingvoltage in the non-selection period Sd is set to 4.5V, regarding boththe ON state for the white display and the OFF state for the blackdisplay. The voltage of the reset pulse Vrp in the second scanningperiod Sf is set to -18V, the voltage of the select pulse Vs is set to-30V, and the OFF setting voltage in the non-selection period Sd is setto -4.5V, regarding both the ON state for the white display and the OFFstate for the black display.

The voltage synchronized with the applied voltage for the scanningelectrode is applied to the signal electrode. The conditions are setsuch that, the voltage 12V is applied in the first phase Sa of the firstscanning period Se in the ON state for the white display, the voltage-12V is applied in the second phase, the voltage -12V is applied in thefirst phase Sb of the second scanning period Sf, and the voltage 12V isapplied in the second phase Sb. Also, the conditions are set such that,the voltage -12V is applied in the first phase Sa of the first scanningperiod Se in the OFF state for the black display, the voltage 12V isapplied in the second phase, the voltage 12V in the first phase Sa ofthe second scanning period Sf, and the voltage -12V is applied in thesecond phase Sb.

Each pulse width is set to 100 μs. As a result, the driving with a framefrequency of approximately 15 ms becomes possible, the frame frequencybecomes much higher than in the case of prior art, and satisfactorydriving becomes possible even with the frequency of the video rate.Thus, in this embodiment, a high speed, complete resetting to theantiferroelectric state in the selection period can be carried out.

Various methods for time-divisionally driving the antiferroelectricliquid crystal element have been proposed as prior arts, and an examplethereof is illustrated in FIG. 18. In FIG. 18, the waveform of thevoltage for setting the ON state for the white display and the OFF statefor setting the black display. In this driving method, the writing ofone picture is carried out in two scanning periods S6 and S7. Thevoltage waveforms in the first scanning period S6 and the secondscanning period S7 are symmetrical each other with regard to the voltage0 volt, so that the alternating effect is intended to be attained by thewriting in the two scanning periods S6 and S7. Each of the firstscanning period S6 and the second scanning period S7 consists of theselection period S4 and the non-selection period S5. The voltage appliedin the selection period S4 consists of three phases: the first phase S1,the second phase S2, and the third phase S3. The synthesized waveform ofthe voltage applied to the scanning electrode and the voltage applied tothe signal electrode is as shown in FIG. 18, in which the resetting tothe OFF state as the antiferroelectric state is necessarily carried outin the first phase S1, the maintenance of the state of the first phaseS1 is carried out in the second phase S2, and the selection whether ornot the state is set to the ON state as the ferroelectric state iscarried out by the select pulse SP in the third phase S3. If the selectpulse SP in the third phase S3 exceed the threshold voltage Vth forsetting to the ferroelectric state, the state is set to the ON state asthe ferroelectric state, and if it does not exceed the thresholdvoltage, the OFF state as the antiferroelectric state is maintained.

The state of the liquid crystal molecule of the antiferroelectric liquidcrystal is illustrated in FIG. 19. As illustrated in FIG. 19, the liquidcrystal molecule M of the antiferroelectric liquid crystal has threestable states. In the case where no voltage is applied, the state is inthe third stable state as the antiferroelectric state, and if thevoltage higher than the threshold voltage is applied, the switching tothe ferroelectric state as the first stable state or the ferroelectricstate as the second stable state is carried out depending on thepolarity of the applied voltage. In the prior art driving method shownin FIG. 18, the applied voltage is made 0 volt to switch from theferroelectric state to the antiferroelectric state. That is, it isarranged that the switching takes place based on the nature, e.g.viscosity, of the molecule itself of the liquid crystal without exertingan external force on the antiferroelectric liquid crystal. Accordingly,the response speed from the ferroelectric state to the antiferroelectricstate is very low.

In the driving method illustrated in FIG. 18, the resetting to theantiferroelectric state is necessarily carried out in the first half ofthe first phase S1 of the selection period S4, and after that theselection whether the state is to be made the ferroelectric state or theantiferroelectric state is carried out by the select pulse SP of thethird phase S3. However, as described above, the response speed from theferroelectric state to the antiferroelectric state of theantiferroelectric liquid crystal is low. Accordingly, if the first phaseS1 as the period for the resetting is short, the completeantiferroelectric state cannot be realized, so that the satisfactorydisplay cannot take place. Therefore, the selection period S4 isrequired to be sufficiently long and, accordingly, the frame frequencycannot be high. As a result, the speed of writing the picture planebecomes slow, so that the driving at the video rate becomes difficult.The relationship between the deflection axis of the antiferroelectricliquid crystal element and the average longitudinal axis direction ofthe liquid crystal molecule is illustrated in FIG. 20. In the methodillustrated in FIG. 20, there are provided at least the first scanningperiod and the second scanning period, the voltage waveforms in thefirst scanning period and the second scanning period are symmetricaleach other with regard to 0 volt, each of the first scanning period andthe second scanning period has at least the selection period and thenon-selection period, the selection period has the first, the second,and the third phases, the reset pulse is applied to the scanningelectrode in the first phase of the selection period, the base voltageis applied to it in the second phase, the select pulse is applied to itin the third phase, the polarity of the voltage of the reset pulse isthe same as that of the threshold voltage for changing from the oneferroelectric state at the time immediately preceding the selectionperiod to the other ferroelectric state, the absolute value of thevoltage of the reset pulse is lower than the absolute value of thethreshold voltage and higher than 0 volt, and the voltage Vbx of thebase voltage is given by the inequality V3<Vbx<V1. In this case, V1 isthe voltage at which the light transmittance starts increasing when apositive voltage is applied to the antiferroelectric liquid crystalelement, V3 is the voltage at which the light transmittance startsincreasing when a negative voltage is applied to the antiferroelectricliquid crystal element, and the polarity of the reset pulse and thepolarity of the select pulse in the same selection period are the same.Preferably, the base voltage applied in the second phase of theselection period is 0 volt.

To switch at a high speed from the ferroelectric state as the firststable state of the liquid crystal molecule of the antiferroelectricliquid crystal shown in FIG. 1 to the antiferroelectric state as thethird stable state, the reset pulse Vrp having a polarity the same asthe polarity of the threshold voltage V6 required for switching to theferroelectric state as the other second stable state and having thevoltage which has the absolute value lower than that of the thresholdvoltage V6 and is higher than 0 volt is applied. To switch at a highspeed from the ferroelectric state as the second stable state to theantiferroelectric state as the third stable state, the reset pulse Vrphaving a polarity the same as the polarity of the threshold voltage V5required for switching to the ferroelectric state as the other firststable state and having the voltage which has the absolute value lowerthan that of the threshold voltage V5 and is higher than 0 volt isapplied.

In the driving method illustrated in FIG. 20, to transfer completely thestate of the liquid crystal molecule which is moved into the vicinity ofthe ferroelectric state as the first or the second stable state to theantiferroelectric state as the third stable state, the base voltage Vbxis applied in the second phase after the reset pulse Vrp is applied. Thebase voltage Vbx is defined by the voltages V3 and V1 which are thevoltages at which the light transmittance starts increasing and have therelationship V3<Vbx<V1, where V1 is the voltage at which the lighttransmittance starts increasing when a positive voltage is applied tothe antiferroelectric liquid crystal element and V3 is the voltage atwhich the light transmittance starts increasing when a negative voltageis applied. The polarity of the base voltage may be optionally selectedand may be the same as or different from that of the reset pulse Vrp.More preferably, the base voltage is 0 volt. In the technique of thepresent invention, regardless of the ferroelectric state or theantiferroelectric state of the state preceding to the selection period,the complete resetting of the liquid crystal molecule to theantiferroelectric state before applying the select pulse Vs in the thirdphase. In this regard, if the base voltage exceeds the above-mentionedrange, the liquid crystal molecule will be transferred to theferroelectric state.

Shown in FIG. 20 the waveforms of the voltages applied to the scanningelectrode and the signal electrode and the synthesized waveform thereofwhen the displays of the ON state for the white display and the OFFstate for the black display are set. In this embodiment, the writing ofone picture is carried out in the first scanning period Sf and thesecond scanning period Sg. The voltage waveforms in the first scanningperiod Sf and in the second scanning period Sg are symmetrical withregard to 0 volt. Each of the first scanning period Sf and the secondscanning period Sg is constituted by the selection period and thenon-selection period. The selection period Sd is constituted by thefirst phase Sa, the second phase Sb, and the third phase Sc. The resetpulse Vrp is applied to the scanning electrode in the first phase Sa,the base voltage Vbx is applied in the second phase Sb, and the selectpulse is applied in the third phase Sc.

In the case where the ferroelectric state for the white display ismaintained, the stable state becomes a different stable state, i.e.either the first stable state or the second stable state, for eachscanning period Sf or Sg. When the state immediately preceding theselection period Sd is the second stable state, the reset pulse Vrphaving the polarity same as that of the threshold voltage V5 for thefirst stable state and having the voltage which satisfies the condition|V5|>|Vrp|>0 is applied. When the state preceding immediately to theselection period Sd is the first stable state, the reset pulse Vrphaving the polarity same as that of the threshold voltage V6 for thesecond stable state and having the voltage which satisfies the condition|V6|>|Vrp|>0 is applied.

In the driving method illustrated in FIG. 20, the base voltage Vbxapplied in the second phase Sb is made 0 volt to return the state of theliquid crystal molecule, which has been moved by the application of thereset pulse Vrp completely to the antiferroelectric state, as the thirdstable state. Thus, by applying the base voltage Vbx represented by therelationship V3<Vbx<V1 after the reset pulse Vrp is applied, thecomplete resetting to the antiferroelectric state can be carried out inthe second phase Sb. Accordingly, the satisfactory high speed displaycan be carried out without depending on the display pattern.

The relationship between the voltage applied to the scanning electrodeand the light transmittance in the selection period Sd of the ON statefor the white display is shown in FIG. 21. The state immediatelypreceding to the selection period Sd is the antiferroelectric state. Itis possible to reset the liquid crystal molecule moved into the vicinityof the ferroelectric state as the first or the second stable state bythe application of the reset pulse Vrp completely to theantiferroelectric state in the second phase Sb by applying the basevoltage Vbx. Accordingly, the light transmittance can be madesufficiently low before the third phase Sc. The relationship between theapplied voltage of the display panel and the light transmittance isshown in FIG. 1. The threshold voltage V5 is 40V, and the thresholdvoltage V6 is -40V.

The reset pulse Vrp is applied to the scanning electrode in the firstphase Sa of the selection period Sd, the base voltage Vbx is applied inthe second phase Sb, and the select pulse Vs is applied in the thirdphase Sc. In both the ON state for the white display and the OFF statefor the black display, it is set that the voltage of the reset pulse Vrpin the first phase Sa of the first scanning period Sf is 18V, the basevoltage is 0 volt, the voltage of the select pulse Vs is 30V, and theOFF setting voltage in the non-selection period Se is 4.5V. In both theON state for the white display and the OFF state for the black display,it is set that the voltage of the reset pulse Vrp in the second scanningperiod Sg is -18V, the base voltage is 0 volt, the voltage of the selectpulse Vs is -30V, and the holding voltage in the non-selection period Seis -4.5V.

The voltage synchronized with the voltage applied to the scanningelectrode is applied to the signal electrode. It is set that 12V voltageis applied in the first phase Sa of the first scanning period Sf in theON state for the white display, 0 volt voltage is applied in the secondphase, -12V voltage is applied in the third phase Sc, -12V voltage isapplied in the first phase Sa of the second scanning period Sg isapplied, 0 volt voltage is applied in the second phase Sb, and 12Vvoltage is applied in the third phase Sc. It is set that -12V voltage isapplied in the first phase Sa of the first scanning period Sf in the OFFstate for the black display, 0 volt voltage is applied in the secondphase Sb, and -12V voltage is applied in the third phase Sc. The widthof each pulse is set to be 100 μm. Thus, the driving can be carried outwith the frame frequency of approximately 15 ms, the frame frequency canbe made fast compared with the case of the prior art, and thesatisfactory display at the frequency of the video rate can be carriedout. Also, regardless of the display pattern, a satisfactory high speeddisplay can be carried out.

In the driving method according to an embodiment of the presentinvention illustrated in FIG. 20, the driving of the antiferroelectricliquid crystal element at the frame frequency of the video rate can becarried out. Also, regardless of the display pattern, a satisfactoryhigh speed display can be carried out.

CAPABILITY OF EXPLOITATION IN INDUSTRY

The antiferroelectric liquid crystal panel and the driving methodthereof according to the present invention can be exploited, forexample, for the display panel, optical shutter array, and the like,using the antiferroelectric liquid crystal having the matrix formingpixels.

I claim:
 1. A method for driving an antiferroelectric liquid crystalpanel which holds an antiferroelectric liquid crystal between a pair ofsubstrates having on opposite surfaces thereof a plurality of scanningelectrodes and signal electrodes and has matrix-forming pixels,comprising:providing one scanning period having a selection period fordetermining the state of a pixel and a non-selection period for holdingthe state of a pixel, and providing a pause period between one scanningperiod and the next scanning period, and making the pixels on all thescanning electrodes simultaneously in the antiferroelectric state duringthe pause period each time the display state of any of the pixels ischanged.
 2. An antiferroelectric liquid crystal display unitcomprising:an antiferroelectric liquid crystal between a pair ofsubstrates having on opposite surfaces thereof a plurality of scanningelectrodes and signal electrodes and having matrix-forming pixels, onescanning period having a selection period for determining the state of apixel and a non-selection period for holding the sate of a pixel, and apause period between the end of one scanning period and beginning of thenext scanning period for making the pixels on all the scanningelectrodes simultaneously in the ferroelectric liquid crystal state eachtime the display state of any of the pixels is changed.
 3. A method fordriving an antiferroelectric liquid crystal display unit which holds anantiferroelectric liquid crystal between a pair of substrates having onopposite surfaces thereof a plurality of scanning electrodes and signalelectrodes and has matrix-forming pixels,characterized in that, theactual driving period of the liquid crystal unit is constituted by atleast two scanning periods, each scanning period includes at least twoperiods: a selection period and a non-selection period, the voltage Vuof the upper limit of the pulse wave applied during the non-selectionperiod is set in the range between the voltage V1 at which thetransmittance starts increasing when a voltage having the same polarityas that of the pulse wave is applied to the antiferroelectric liquidcrystal unit and the applied voltage is increased and the voltage V2 atwhich the transmittance starts decreasing when the applied voltage isdecreased, i.e. V2≦Vu≦V1, and the voltage Vd of the lower limit of thepulse wave is set in the range between the voltage V3 at which thetransmittance starts increasing when the absolute value of the voltagehaving the polarity opposite to that of the voltage V1 is increased andthe voltage V1, i.e. V3≦Vd≦V1.
 4. A method for driving anantiferroelectric liquid crystal element in which there are provided atleast a first scanning period and a second scanning period, the voltagewaveforms in said first and second scanning periods are symmetrical withregard to 0 volt, and each of said first and second scanning periods hasat least a selection period and a non-selection period,characterized inthat, a reset pulse is applied to the scanning electrodes in the firstphase of said selection period, a select pulse is applied to thescanning electrodes in the second phase of said selection period, thepolarity of the voltage of said reset pulse is the same as that of thethreshold voltage for changing the one ferroelectric state preceding tosaid selection period to the other ferroelectric state, the absolutevalue of the voltage of said reset pulse is higher than 0 volt and lowerthan the absolute value of said threshold voltage, and the polarities ofsaid reset pulse and said select pulse in said same selection period arethe same.
 5. A method for driving an antiferroelectric liquid crystalelement in which there are provided at least a first scanning period anda second scanning period, the voltage waveforms in said first and secondscanning periods are symmetrical with regard to 0 volt, and each of saidfirst and second scanning periods has at least a selection period and anon-selection period,characterized in that, said selection period has afirst phase, a second phase, and a third phase, a reset pulse is appliedto the scanning electrodes in said first phase of said selection period,a base voltage is applied to the scanning electrodes in said secondphase, a select pulse is applied to the scanning electrodes in saidthird phase, the polarity of the voltage of said reset pulse is the sameas that of the threshold voltage for changing the one ferroelectricstate preceding to said selection period to the other ferroelectricstate, the absolute value of said reset pulse is higher than 0 volt andlower than the absolute value of said threshold voltage, and the voltageVbx of said base voltage is given by the inequality: V3<Vbx<V1, where V1is the voltage at which the transmittance starts increasing when apositive voltage is applied to the antiferroelectric liquid crystalelement and V3 is the voltage at which the transmittance startsincreasing when a negative voltage is applied thereto, and thepolarities of said reset pulse and said select pulse in said sameselection period are the same.
 6. A method for driving anantiferroelectric liquid crystal element according to claim 5, whereinsaid base voltage is 0 volt.
 7. An antiferroelectric liquid crystaldisplay unit comprising:an antiferroelectric liquid crystal between apair of substrates having on opposite surfaces thereof a plurality ofscanning electrodes and signal electrodes and having matrix-formingpixels, one scanning period having a selection period for determiningthe state of a pixel and a non-selection period for holding the state ofa pixel, a pause period between one scanning period and the nextscanning period for making the pixels on all the scanning electrodessimultaneously in the ferroelectric state, and a driving circuitconnected electrically with the antiferroelectric liquid crystal paneland constituted by two circuits: a display drive waveform outputtingcircuit and a layer structure control outputting circuit for controllingin cell the layer structure of a smectic layer, and whereby a selectionof the outputs of said two circuits is carried out.
 8. A method fordriving an antiferroelectric liquid crystal display unitcomprising:providing an antiferroelectric liquid crystal between a pairof substrates having on opposite surfaces thereof a plurality ofscanning electrodes and signal electrodes and having matrix-formingpixels, providing a scanning period having a selection period fordetermining the state of a pixel and a non-selection period for holdingthe state of a pixel, and providing in the scanning period a resetperiod for causing the state of a pixel to be reset always to theferroelectric state regardless of the current state of the pixel.